The morphological characters of mammalian sperm cells taken from the ductuli efferentes differ only slightly from the sperm derived from the vas deferens. However, it is known that spermatozoa from the caput epididymis, when kept in physiological salt solution, quickly become immotile, whereas those from the cauda epididymis retain their motility for a long time (Moore, 1928). During the slow passage through the epididymis the spermatozoa undergo a physiological process of maturation, which is said to occur under the influence of the epithelium of the epididymis and to result in a lesser susceptibility on the part of the spermatozoa to extraneous influences (Braus and Redenz, 1924; Redenz, 1926; and Lanz, 1929). Other authors maintain that this maturation of the spermatozoon is not conditioned by environmental influences (Young, 1931). In any case the spermatozoa achieve full functional ability only after they have reached the cauda epididymis and the vas deferens. These are the spermatozoa which enter the female genital tract at copulation, and thus it follows that spermatozoa for artificial insemination in the mouse must be taken from the vas deferens and cauda epididymis.
